This proposal is aimed at understanding the function of the gene that is mutated in the human disease Neurofibromatosis type1. The disease is characterized by a wide variety of pathological manifestations (e.g. tumors, pigmentation changes, behavioral abnormalities, growth defect) and the basis of many of these is not known. The prevailing view of NF1 function is that it is primarily a negative regulator of the Ras GTPase by acting as a GTPase activating protein (GAP) for Ras. To study the function of NF1 in vivo in an organism amenable to genetic manipulations, a highly conserved Drosophila homologue was cloned and characterized. Studies with the Drosophila NF1 homologue have failed to show evidence of altered Ras1-mediated signaling in NF1 mutants suggesting that the postulated role of NF1 as a Ras1 regulator ma either be redundant or less important in vivo. In contrast strong genetic interactions were observed between NF1 and genes encoding components of the cAMP/PKA signaling pathway. NF1 mutants show defects in growth and in synaptic transmission. The growth defect is rescued by a mutant protein that lacks GAP activity and appears to require a non cell autonomous function of NF1. The experiments described here are aimed at elucidating the apparently Ras1- independent functions of the NF1 gene and its role in regulating growth via a non cell autonomous mechanism. Specific Aim 1 is to provide a detailed description of how NF1 regulates growth in vivo. Included is an analysis of the interaction between NF1 and the cAMP/PKA pathway. Specific Aim 2 is to define the signaling pathways that mediate Ras-independent functions of NF1 in vivo by identifying domains in the NF1 protein that interact with other pathways. Specific Aim 3 is to identify genes that interact with NF1 in vivo. These will be identified either by a genetic screen for enhancers and suppressors of the pupal size phenotype of a hypomorphic NF1 allele or by using a microarray of cDNA clones and looking for significant alteration in gene expression in NF1 mutants. These studies will help us understand the normal function of the NF1 gene in vivo and will contribute to our understanding of the diverse manifestations of the disease process.